Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

571
FXUS63 KLOT 202326
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
626 PM CDT Wed May 20 2026

.KEY MESSAGES...

- Showers likely late Friday into Friday night.

- Return to somewhat above average temperatures expected next
  week, though cooler temperatures expected near the lake.

&&

.DISCUSSION...
Issued at 202 PM CDT Wed May 20 2026

High pressure over Lake Superior providing for northerly winds
and a steady feed of rather chilly temperatures, especially near
and just downwind of Lake Michigan. Thursday looks to be pretty
similar to today, though with more mid-high level cloudiness
northern CWA and with slightly less wind. While the winds won`t
be quite as gusty, they`ll remain off the lake and keep temps in
the 50s again near the lake. Southern CWA, where there should be
a bit more sunshine, should see temps several degrees warmer
than today, probably making a run at 70 degrees.

Shortwave trough over northern Mexico is progged to lift
northeastward into the mid-Mississippi to lower Ohio valley
regions Friday into Friday night. Associated sfc low is progged
to track from central IL northeast into lower Michigan Friday
night with the warm sector expected to remain south of most, if
not all, of our CWA. Rain associated with this system is progged
to begin spreading into our southern CWA during the afternoon,
spreading north to the WI border early Friday evening. As
mentioned in the previous AFD, instability is expected to
remain well south of our CWA with seemingly very little threat
of thunderstorms, so we`re looking for primarily just a chilly
rain.

Given the currently progged track of the sfc low, it is possible
that our extreme southeast CWA could briefly poke into the warm
sector Friday evening. Despite this, GFS and ECMWF forecast
soundings exhibit little or no CAPE due to the rather cool low
levels and warmer than average mid-level temps (-8 to -10C at
500mb). Opted to only retain the slight chance of thunderstorms
Friday evening over the far southeast corner of our CWA and even
there the chances appear meager.

Rain should end by or shortly after sunrise Saturday, but
lingering cloud cover will likely keep temps from getting too
warm. Winds off the lake will again keep it chilly near the
lake. Fast on the heels of this southern stream shortwave will
be a northern stream shortwave wave by Sunday. Warm air
advection ahead of this wave should result in warmer temps
Sunday, possibly right up to the lakefront. NBM pops were
pretty low Sunday and didn`t make any changes at this time,
given some model variability in handling of this system as well
as the progged weaker forcing and questionable moisture. This
will be something we`ll have to look at in coming days to see
how models trend with that wave.

Medium range guidance is in pretty good agreement on a large
scale pattern change over North America next week. Both EPS and
GEFS develop high amplitude, high latitude upper ridging over
central Canada south into the north central U.S. with a
developing omega block pattern. Medium range guidance can
struggle at times in dealing with blocking patterns, but the
signal has been and continues to be pretty strong. This would
likely result in warmer than average temperatures and likely
drier than normal conditions locally. However, the northern
displacement of the upper ridge would probably mean a surface
high to our north as well, which would open to the door to winds
off Lake Michigan and the typical spring/early summer "cooler
near the lake" forecast for much of next week.

- Izzi

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 626 PM CDT Wed May 20 2026

NE winds will prevail tonight, with gusts becoming less frequent
through the evening. Winds will then veer E or even briefly SE
late tonight and into Thursday morning. As this occurs, MVFR
cigs may slosh westward across the terminals. Confidence remains
a bit too low to warrant prevailing or TEMPO groups for MVFR
cigs but will continue to monitor.

An increase in mid-level moisture is forecast to occur Thursday
morning, particularly near RFD as a weak disturbance transits
the area. Can`t rule out the potential for a few sprinkles or
even some showers, but chances remain too low for a precip
mention given lingering sub-cloud dry air.

A secondary front/lake breeze will reinforce gusty NE winds
Thursday afternoon before winds once again ease Thursday
evening.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through Thursday afternoon for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement through Thursday morning for INZ001.

     Beach Hazards Statement through Thursday morning for INZ002.

LM...Small Craft Advisory until 1 PM CDT Thursday for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CDT Thursday for the IN
     nearshore waters.

&&

$$

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